Power-line signaling



oct. 19,1926, n,603,651

v W. v. WQLFE.

POWER LINE SIGNALING Filed Apri '7l 1924 3 Seis-Sheut 1 W. V. WOLFE POWER LINE SIGNALING Filed April 7, 1924 5 sheets-Shet s r /rksbx/w Patented Oct. 19, 1926.

UNITED, STATE-s PATENT OFFICE.

WALLACE V.. WOLFE, 0F GLEN RIDGE, N'E`W JERSEY, ASSIGNOR T0 WESTERN ELEC-v TRIO CQMPANY, INCORPORATED, 0F NEW YORK, N. Y., A CORPORATION OF NEW YORK.

A'.PWER-LINE SIGNALING.

Application led April 7, 1924. Serial No. 704,614.

This invention relates to communication by means of high frequency waves, and more particularly to communication over power lines by superimposing the high frequency waves upon the power currents .traversing the power line. 4

An object of the invention is to provide for `full duplex telephone communication over power lines.

Another Objectis to provide for full duplex telephone communication over power transmission lines in which the transmitting volume will be sufficient for transmission under both normali and abnormal conditionsA over either long or short lines, in which a full metallic high frequency circuit is employed in order to 'avoid the numerous diiiculties connected with ground return circuits, and furthermore, to employ for communication such carrier frequencies as will not interfere with existing communication systems vand particularly with carrier wave telephone systems parallel with the ower lines. An ancillary object is to avoi any interference of 4harmonics of the power line current, static or other impulsive disturbances, and other communication systems, with the power line signaling system.`

A special object is to provide means for effectually centralizing the energy supply for the transmitting and receiving devlces of a duplex telephone system.

An important object is .to provide for safely and efiiciently couplin high frequency signaling apparatus to igh voltage transmission lines.

In a particular embodiment any desired' number of high frequency translating stations, two or more, are coupled to two conductors of a three-phase transmission line operating at a voltage of the Order 0f 110,000

volts. To each station is connected a local telephone circuit Ain which is connected one or a greater number of telephone stations. The equipment ateach high frequency sta.- tion includes high frequency translatin ap- .paratus for enerating, modulating, an amplifying hig .frequency waves to be transmitted to the power line, and for amplifying and detecting modulated high frequency waves received therefrom. It also includes selective circuits by means of which the incoming and outgomcr waves are conned to separate channels wlthin the station, and a coupling circuit through which the high freuency apparatus is connected to the power hne and which is especially adapted to prevent the voltages of the power currents entering the translating station. The local telephone circuit is connected to the translating station through a bridge or hybrid coil by means of which the outgoing and incoming currents are separated and-diverted to channels passing through the transmitting and the receiving apparatus respectively.

Separation of the low frequency incoming v mits duplex communication over the system.

Two carrier Ifrequencies are used for the high frequency transmission, one of which is always used for transmitting by any station originating a call and the other of which is always used by a called station in replying.'V The selective circuitsv at each station are adapted respectively to transmit these frequencies; normally, that is in the idle condltion of the station, the receiving ap aratus. is connected to the selective cir cult that is adapted to transmit the frequency allocated to the calling station and relays are provided by means of which the selective circuits are lnterchanged at a call originating station before communication begins. Station selection is accomplished by means of a well known type of selector hereinafter described, which is combined with the high fre uency circuit in such a manner to be proper y actuated by incoming waves.

A high degree of protection of the high frequency apparatus and of the users of the tele hone system against the high voltages of 151e power line is secured by the special features of the coupling circuit by means of which -the apparatus is connected to the iol of impedance elements which are mounted within the same buildin as the high frequency apparatus and which have associated with them low voltage rotective devices. Another part comprises "gli voltage com' densers and hi h voltage protective devices mounted outs'i e the station building.

The invention will be more fully under- .stood both as to the details of its or anization and its mode of operation by re erence to the following description taken in connec- 'tion with the accompanying drawings, of

'which- Figs. land 2 constitute a circuit diagram showing the essential features of the apparatus employed at one station and in its as- J sociated local circuit, and

Fig. 3 shows a possible layout of the several groups of apparatus constituting the couphng circuit. p

In the circuit shown in Figs. 1 and 2, 4 is a low frequency telephone circuit to which may be connected four telephone stations two of which, 1 and 2, are shown in complete circuit detail, and the connections to the others are indicated by the branch circuits 66 and 67. Station 1 is that of the operator or party located at the translating station; station 2 and the others may be located at points remote therefrom. In effect the four local stations are connected in par-l allel between the two sides 0f the circuit 4.

The equipment of station 1, which will hereinafter be designated the operators station, differs principally from that of the other stations, hereinafter referred to as extension stations, in that a separate battery is provided at the extensions for ringing and for operating the microphone, whereas at the operator s station use is made of a common battery which provides also energy for space discharge devices and for relays in the common local circuit. To isolate the batteries at the extension stations, the branches leading thereto are connected through condensers 6, which have large enough capacities to pass the speech currents freely. The low frequency circuit is connected to the high frequency translating apparatus by means of bridge transformer 5, one output circuit of which includes the high frequency transmitting apparatus and the other the receiving and detecting apparatus, separate incoming and outgoing channels for the signaling currents being thus provided within the translating station. The outgoing channel includes the apparatus for generating and transmitting modulated carrier waves, comprising ,a signal or speech amplifier 8, a high frequency oscillator 7, a modulator 9, and an auxiliary ainyplitier 10 adapted to amplify the modulated iigh frequency 'wa-ves produced by the modulator9. Ordinaril the amplifier 10 is not used, being rovide for emergency use as vhereinafter escribed, and the outgoing channel is normally continued from the output of the modulator through the contacts of relay 40 to a highass filter 11 which is adapted to transmit t ie higher of the carrier frequencies and to suppress the lower. rl'he incoming circuit includes a multi-stage high frequency amplifier 15, a detector or `deinodulator 16, and in its normal condition includes also a low-pass filter 12 which is adapted to transmit the lower frequency carrier wave and to suppress the higher. For calling purposes, the incoming channel is extendedfroni the output of the detector by means of relays through a separate channel to call signal devices at the several local telephone stations. This call signal channel includes a multi-position selector 17 to which are connected individual signal circuits 47, 48, 49 and 5() leading to the local circuit telephone stations. The selector 17 is the type of device described and claimed in the patent to J. C. Field, No. 1,343,256, granted June 15, 1920.. J`

A. common source 56 is provided for the space current required by the space discharge devices 7, 8 and 9 of the transmitting apparatus and the amplifiers and detector of the receiving apparatus; the filamentary cathodes of these discharge devices are also supplied with energizing current from a separate common".l source 68. The control electrodes of the receiving devices are polarized by being connected to points of suitable potential in the cathode circuit. In the transmitting apparatus, larger polarizing potentials are required than can be obtained from the cathode circuit alone and these are provided in part by the potential drop in a resistance 57 which is inserted in the space current circuit between the negative terminals of the cathode current source 68 and space current source 56, and in part by the fall of potential in the cathode circuit. By this means, full advantage is taken of the potential difference necessary for the heating of the filaments and the additional potentials required are secured at the cost of a minimum expenditure of, energy and with the advantage of the elimination of separate polarizing batteries.

l't is commonly the case in the operation` of systems of this type that a station may be idle for relatively long periods and it is desirable that the energy required to operate the apparatus be conserved during such periods. IThe receiving apparatus must continuously be ready to receive incoming calls and for this reason the space discharge tubes must becontinuously energized. The greater amount of energy, however, is taken by the discharge tubes of the transmitting apparatus, and this may be saved by decnergiz- :t

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the common branch of the ,space current supply circuit, the establishment of the space current in the transmitting devices would cause a drop in the potential applied to the receiver anodes and an undesirable change of sensitivity in the receiver. To prevent this, the receiver dischar tubes are operated at a potential somewhat lower than that of the transmitter, the reduced potential bein secured by means of resistances 58 and 59 wghich are inserted in the separate space current circuit to the receiver, and a relay circuit is provided which simultaneously with the establishment of the space current in the transmitter short circuits the resistance 58, thereby maintaining the re ceiver anode voltage and space current at steady values.

For ecient signaling it is essential that the signaling circuit be connected with the.

power line in such a manner as to elect a suitable transfer of energy from the signaling circuit to the line and from the line to the signaling circuit. For protection of the signaling apparatus and persons communieating thereover, it is essentialthat direct contact with the high 'voltage lines be avoided. rlhe cou lingpcondensers 14 may comprise any suitab e arrangement whereby a capacity of a sulliciently large value is provided between the terminals of the signaling circuit and the conductors oi the ower line. Such a capacity may be provi ed by a fixed condenser adapted to withstand the high voltages or an arrangement ol. aerial Lll) wires arranged adjacent to the power linev conductors. lt has been proposed to employ a section of high voltage cable, the cord ot which constitutes the power line conductor and the sheath of which serves as a 'plate of a condenser to which the signaling circuit is connected. However, the manufacture ont cable adapted to continuously' withstand the high voltages met with is a matter of considerable ditiiculty. 'lFh'e preferred coupling .arrangement 'consists of fixed condensers having an oil dielectric or a composite dielectric com rising plates ot glass immersed in oil, and being contained in substantial waterproof metal tanks provided with high voltage insulators of such type as is commonly used in high voltage out-door installations. rlihe coupling circuit comprises condensers 19 and choke coils 20 in series with the line and condensers 2l and choke coils 22 in shunt to the line. The coils 22 serve also to shunt to ground any '60 cycle current entering the coupling circuit. Choke coils 23 are connected in the .line adjacent the coupling condensers i4. Safety devices com rise fuses 24:', open air spark gaps 25 and 26 Iof high current capacity and vacuum gap 27 in shunt to the` gaps 26.

- gaps.

The vacuum gap breaks down ui'ckly under the influence \of excessive vo tages, and thus serves to protect the signaling circuit4 until the air gaps 26., which are adapted to carry a much heavier current than the vacuum gap, come into operation. Fuses 62 and disconnecting switches 61 are provided between the choke coils 20 and 23 for additional protection and to permit the high frequency apparatus being disconnected from the powerline. Further-protection `of the high frequency apparatus. is furnished by the protective device 60 inserted between the channel filters and the coupling circuit. This device is the type commonly used for the protection of telephone stations and comprises fuses inserted in the line and klow voltage bridging discharge Part of the coupling circuit is installed within the building used'to house the high frequency apparatus, the enclosing wall of the building being indicated .at 63 into which are built high voltage insulators 64 for the outgoing leads. A. second part 'including choke coils 22 and 23 and con densers`21 is mounted within a closed compartment 65 which is mounted outside the station building. including the liigh voltage condensers 14 and discharge gaps 25 `are mounted outdoors adjacent to the power line Without additional protection against the weather. A possible physical organization of the coupling circuit is shown in Fig. 3 in which the 'numerals designate the same elements as they designate in Figs. le and 2. Illhe arrangement is shown in elevation, duplicate elements not being shown. The. compartrnent 65 containing the intermediate group of elements is mounted on a pole 7l on which is also vmounted the open air discharge gaps 25, one pole of which is connected to ground The remaining elements IUU through conductor 76. ithin the building the station ap aratus is mounted on vertical panels 69, t e ligure showing an end elevation ot these.

@parution in calling from operators station.

When the operator at station l takes his receiver from the switchhook, the contact 32 lli) is closed., thereby connecting ground Ato the conductor 33. `The relays 34C, 35 and 36 theny operate. battery to be applied to conductor 72 and since the circuit ot selector key SK is norl 'llhe operation of relay 35 causes suined that line conditions are normal and that the auxiliary amplier 10 is not to be used., in which case the switch 51 is closed inthe lett hand position. rihe relay 36 closes he filament heating circuits of the space ischarge devices 7, 8 and 9 and also ot the auxiliary amplifier l0. The heating ot the. laments in the devices' 7, 8 and y the code.

,space current in the transmitter.

causes the space current circuits therefor to be completed, current being sup lied fromy the source 56 and the devices eing then completely energized. The operator now actuates one of the keys SK corresponding to the stationfhe desires to call. The operation of the selector key alternately opens and closes a short circuit around the relay 37 in accordance with a predetermined code and thereby causes the condenser 38 to be added to the oscillating circuit of the oscillator intermittently in accordance with Normally, the high-pass filter 11 is connected to the transmitting channel and the low-pass iilter 12 is connected to the re ceiving channel. However, the operation of the relays 40 and 4l following upon the operation'of relay 34 causes theiilters to be interchanged so that the low-pass filter 12 is connected to the transmitting circuit.

During the operation of the selector key, the frequency generated by the oscillator l is thus changed back and forth from the low carrier'fre uency to the high carrier frequency, kan vice versa. -However, the high carrier frequency is not transmitted to the line inasmuch as the low pass filter suppresses it, the result being that'groups of waves of the low carrier frequency alone are transmitted to and impressed uponthe power line. lllhen the selected station answers, the operator may converse, by means of his telephone set, with the party at the selected station. The operation of the selector key is prevented from adecting the relays 40 ,and 41 by the resistance 73 which isv included in the circuit of relay 37 but which is not short circuited by the key. ln addition to operating relay 36 and coinu pleting the circuits of relays 37, 40 and 41, the operation of relay B causes a short circuit to be placed around the resistance 58, thereby annulling-the effect on the receiver space current due to lthe establishment of It further places a short circuit around the marginal relay 42, thereby preventing incoming carrier waves from adecting the established condition of the calling station. The station originating Aa call always transmits on the lower of the two carrier frequencies and receives on the higher. lf desired, the high frequency may be used for calling and the lower for answering.

Operation n calling from om extension station'.

ing the relays and 35at the translating.

station to' operate, in sequence. The opera- :neonata tion of relay' 35 conditions the high frequency apparatus for transmission as already described in connection with the operation in calling from the operators station. The operator now actuates one of the keys SK correspondin to the station he desires to call, thereby intermittently grounding the conductor 7 6 in accordance with vthe predetermined code. Relay 31 at the translating station is thus intermittently o erated, following the code of the selector ey and creating an intermittent short circuit around the relay 37 also in" accordance with the impulses created by the selector key. ln other respects the operation of the system from a remote station is the same as the operation from the dperators station.

@parution at a called station.

ll`he electrode circuits of the amplifier 15 and the detector 16 are normally energized. lncoming high frequency Waves are detected by the detector 16, causing an increase in the Aspace current thereto and operating the marginal relay 42, provided that the called station is idle. lf, however, the called station is not idle, the relay 42 could. not operate on account of the short circuit placed around it by the operation of relay as hereinbefore described. The operation of the relay 42 causes relay 43 to operate and the relay 44 in sequence, the circuit of relay 44 being completed through the left hand contact of relay 43. lncoming groups of waves deter mined by the selector key at the calling station cause the relays 42, 43 and'44 to operate and the selector 17 to step in accordance with the code of the received impulses. The stepping of the selector 17 causes the Contact arm 77 to select one of the lines 47, 48, 49 or 50, thereby connecting it to ground momentarily through the spring contact 78. lf the line 47 is selected corresponding to the operators station, the momentary connection to ground causes lock-up relay 28 to operate and the signal bell 18 to ring. lf the line selected is 48 corresponding to the extension station 2, a similar lock-up relay is operated. Battery is applied to a third conductor 79 extending to the remote station and terminating in a relay 29, the operation of which closes a local circuit, thereby operating a signal bell. After the code signals have been transmitted and While the callin operator is awaiting the response of the ca led party, a continuous train of Wavesof the lower carrier frequency is being` received by the detector 16 and the marginal relay 42 is maintained continuously operated. ln the absence of impulses, the selector 17 is restored to its normal position and the momentary ground is removed from the selected circuit. However, by virtue of the lockup feature of the ringing relays 28, a

'Ill

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"called station. When station 1 is called and the operator removes hisreceiver from the hook and places ground upon the conductor '33 the operation of relay 34 breaks the eircuit ofthe lock-up relay 28, thereby stopping the ringing signal. The operation of relay 35 follows in sequence after the operation of relay 34,v but yon ,account of the relay 43 being operated the functions that the relay 35 can perform are limited to short circuiting the resistance 58 and causing the operation of relay 36 to energize the transmitting apparatus. Relay 37 remains unoperated, whereby the oscillator 7 is caused to generate waves of the higher carrier frequency. Rela s 40 and 41 also remain unoperated w ereby the high-pass filter remains connected to the `transmitting apparatus and the low-pass filter to the receiving apparatus. The called station thus always transmits on the higher of the two carrier frequencies and receives on. the lower. ,Of course, the use of the frequencies may be the reverse of that stated, if desired.` If the called station is an extension station, such as 2, the removal of the receiver from the switchhook in response to the call by closing the contact 7 4, energizes the relay 45 at the extension station and in sequence the rela 30 at the translatingstation. Relay 30, functioning in the same manner as relay 34, breaks the circuit of the lock-up relay, thereby stopping the bell at the extension station and at the same time operates relay 35. ln this case, the further operations are the saine as described in connection with the response ot station 1 to an incoming call.

Operation at an idle station.

When oscillations ot the frequency used by a call originating station` are impressed upon the line, the relays 42, 43 and 44 are actuated once for each group of waves. However, as the arrangement of the o'ups is not one of those for which the selector 17 is set, the selector does not close any of the call signal circuits and at the cessation of the incoming impulses returns to its normal position. lin order that the party at one of the idle stations wishing to make acall may avoid breaking in on a conversation that is already in progress, it is desirable that means be rovided to indicate when the line is busy. n the system described, this indication is provided in the form of an audible busy signal. 'lilie receivers of the several telephone setsassociated with a translating station are permanently connected in circuit, so that any conversation that is taking place over the "system is made audible atall stations without the receiver having to be renuovedy from the switchhook. Uperators at idle stations are thus warned'notto attempt togcall upon the circuit whereby they are j able to avoid .interfering with conversa,

tions in progress.

I Emergency key operation.

1f line conditions are too abnormal to allow code selective ringing, if the selector circuits are not operating pro erly, if there are only two stations upon t e line, or, if it isdesided to arran e so that all the stations may be called simultaneously from a. chief operators station, the key 46 may be operated. High frequency impulses put upon the line will 4then cause the rela 43 to close a circuit directl through al of the locking relays 28 an the lines 47, 48, 49 and 50, which have been connected together, thereby causing a simultaneous ringing signal at all of the local stations.

Auzviliary amplifier circuit operation. If line conditions vare bad owing toa break in the line or a section of the line bep ing down, the switch 51 is moved from its -nornialleft hand position to the right hand y fier 10 through t e high frequency transformer 55 and the high or low pass filter 11 or 12, as the case may be, to the line. Closing the switch 51 in its right hand-position connects a power source 52 to a motor generator 53 which furnishes space current to the power amplier 10. The filament current of the amplier 10 is furnished from the coon source 68 and is controlled as hereinbefore described by the relay 36. The amplier 10 is ot a type capable of supplying iroin tive to twenty times more energy than is normally used forl transmitting.

lt is contein lated that the coupling circuit 13 should have the transmission characteristic of a very atly tuned circuit or preferab that it should have the characteristic of a andvpass lter, thus transmitting with cies from 80,000 to 100,000 cycles per second i or whatever frequencies are used in the particular system. A band pass iilter asses a band ot frequencies with substantie ly uni- -forni and small attenuation and greatly discriminat/es against currents of other frequencies. Such a band filterl characteristic may be obtained by properly choosing the capacities 19 and 21, inductances 20, 22 and 23, and the capacities 14. An advantage of a band pass tilter in this connection is that it discriminates not only a ainst the low frequencies of the power ine, but also against high frequency waves such as may be picked'up by the interception of radio signals or by the action of atmospheric static discharges.

A teature of the local circuit is the use of the artificial line 55 in series with the operators telephone station. The purpose of this line is to limit the amount of energy received at the local station to about the same value as that received at the remote stations, whereby uniform transmission is secured at all points. v

An additional feature of the operation of the system is that the party at any one of the stations of the local circuit connected to a translating station may call any of the other stations in the same local circuit. Calling is accomplished in the same manner as calling a distant station, a selector key correspondin to the code signal ot' the local station ca led being operated. rll`he operation of the selector key places a ground on the circuitincluding the selector operating relay 44', either directly if the calling station is the operators station 1 at the translating station or indirectly throu h the contact ot relay 3l itt the call originates at station 2 or another of the extensions.

1What is claimed is:

l. signaling system comprising a high frequency transmission channel, a 'wave translating system connected to deliver high frequency wave energy thereto, a control circuit operatively associatedv with the translating system to condition it for the production of high frequency waves, a second control circuit adapted to control the frequency of the high frequency waves, a two wire line extending from the translating @stem to a remote low frequency wave signaling system, the conductors of said two wire line being conductively isolated from each ether, and relay circuits operatively connected with each oit said control circuits to extend the control ot the translating station to the remote signalling station, each relay circuit including respectively one conductor ot the said two wire line.

2. t power line signalin system comprising a power transmission ine, a high frequency wave translating system connected thereto and including a space discharge oscillator a source of power for said oscillator, a telephone line connected to said translating station and extending to a remotetelephone station, a relay circuit adapted to`conneet said oscillator to said power source, and a secondrelay circuit adapted to control the frequency determining elements of the oscillator, the conductors yof said telephone line being conduotively separated from each other and included respectively in said relay circuits whereby the control of the translating station is extended to the remote telephone station.

c 3. A power line signaling system comprising a power transmission line, `a high trequency wave translating system connected thereto, a control circuit operatively associated with the translating system to condition it for theJ production of high frequency oscillations, a second control circuit adapted to control the frequency of the high frequency oscillations, a plurality vof telephone lines connected together in parallel and extending from said translating system to 'a like plurality oit remote telephone stations, the conductors of said lines being conductively insulated from each other, and relay circuits corresponding to each of said lines, operatively associated with each ot said control circuits and extended in pairs to the remote control stations through the separate insulated conductors of the lines.

d. ln a signaling system in accordance with claim 2, a telephone receiver at Said telephone station, said receiver being continuously connected to the telephone line recited in claim 2 whereby a busy condition of the circuit is audibly indicated.

5. in a twofway signaling system, transinitting apparatus and receiving apparatus including space discharge devices, a common source of space current for said devices, means for changing in intensity the space current to said transmitting apparatus and additional means rendered effective upon the actuation of said intensity changing means to annul the edect of the changes upon the space current ot said receiving apparatus.

6. "In a signaling system, transmitting apparatus and receiving apparatus including space discharge devices, space current cirl cuits connected to said devices and to a common current source, said space current circuits including a common branch containing an impedance, means for independently interrupting the space current to said transl initting apparatus, and additional means rendered eiiective upon the operation or" said interrupting means for annulling the eiiect of said interruption upon the space current of said receiving apparatus by changing in a compensating manner the impedance of the supply circuits therefor.

7. in a signaling system, transmitting apparatus and receiving. apparatus including space discharge devices, space current circuits for said transmittin apparatus and receiving apparatus inclu ing a common current source and having a common path containing as impedance, the space current circuit for said transmitting apparatus being normally interrupted and the space current circuit for the receiving apparatus being continuously closed, a second impedance ineluded in an independent branch of the space current circuit of the receiver, means for independently establishing the space current to said transmitting apparatus Aand additional means, effective upon the operation of said first mentioned means to short cir, cuit said second impedance.

8. In a signaling system a signal modifying apparatus comprising a p urality of space discharge devices having control electrodes and filamentary cathodes, a. source of heating current for said cathodes, and a source of space4 current for said discharge devices, at least one of said control electrodes being negatively polarized with respectto its cathode in part by the potential of said lheatin source and in partby the potential of sai space current source.

9. In a signaling system, a signal modifying apparatus comprising a plurality of space discharge devices having control electrodes and ilamentary cathodes, said cathodes and source of' heating current therefor beingconnected in a series circuit, a space current circuit connected Ibetween the anodes of said devices and a point in the cathode heating circuit, a source of current included in said circuit, a resistance included between the cathode circuit and the negative terminal of said source, and conductive circuits connecting said control electrodes to said resistance f trodes is polarized with respect to its associated cathode in part by a potential drop 1n the cathode heating current and in part by a potential drop in the space current circuit.

10. In a system for signaling over high voltage power lines, a station building contaming high frequency translating apparatus, a high Volt-age power line outside said building, and a broad band filter for coupling said high frequency apparatus .to said power line, said filter comprising a plurality'of groups of impedance elements, one of said groups including terminal condensers adapted to be connected to said line and to withstand the voltages thereof and being located adjacent thereto outside said building, another of said groups being located Within said building, and each of said groups including voltage operated protective devices.

In witness whereof, l hereunto subscribe my name this 5th day of April A. D., 1924.

WALIniClll V, WOLFE. 

